1. Field of the Invention
The present invention relates to an apparatus for and a method of inspecting a sheet body, and more particularly to an apparatus for and a method of inspecting a sheet body to detect a bend in the sheet body or a defect such as an irregularity of the thickness of a coated agent on the sheet body.
2. Description of the Related Art
A sheet body, such as a photographic film, for example, is manufactured according to a process including several steps as shown in FIG. 11 of the accompanying drawings.
The manufacturing process shown in FIG. 11 will be described below. In step S501, a sheet body serving as a film base is fabricated and wound around a core 500. Then, in step S502, the sheet body is unreeled from the core 500, coated with a photosensitive emulsion (silver halide or the like), and wound around another core 501.
Thereafter, in step S503, the sheet body coated with the photosensitive emulsion is severed to a suitable width and wound around another core 502. In step S504, the sheet body is cut off to product dimensions, inspected, packaged, and then shipped as photographic films.
As shown in FIG. 12 of the accompanying drawings, the sheet body as the film base has an end 400 that starts to be wound around the core 500. Since the end 400 provides a step due to its own thickness on the core 500, sheet coils wound around the end 400 are bent over the step. The bends of those sheet coils are progressively greater toward the core 500 and progressively smaller away from the core 500. The produced sheet body is cut to a given length and wound around the core 500 while the sheet body is being fed. Therefore, the end 400 of the sheet body is inclined to the axis of the core 500 depending on the speed at which the sheet body is fed when it is cut off and the speed at which the sheet body is cut by the cutter.
As a result, as shown in FIG. 13 of the accompanying drawings, the sheet body wound around the core 500 has a plurality of deformed areas 450 due to the bends in the respective sheet coils around the core 500 successively from the end 400, the deformed areas 450 being inclined at an angle φ to the axis of the core 500. The deformed areas 450 manifest themselves more greatly toward the core 500.
When the sheet body with the deformed areas 450 is coated with a photosensitive emulsion, the deformed areas 450 and other areas are not uniformly coated with the photosensitive emulsion. If the thickness of the applied photosensitive emulsion is not uniform, then images recorded on the photographic film tend to suffer density irregularities. Consequently, the deformed areas 450 need to be discarded as defective areas.
One conventional process of automatically detecting such defective areas of a sheet body is disclosed in Japanese Laid-Open Patent Publication No. 2-216437, for example. According to the disclosed conventional process, a parallel beam of light is applied to a light-transmissive sheet body, and a change in the amount of light that has passed through the light-transmissive sheet body is detected. If the light-transmissive sheet body has a defect such as a recess, the applied parallel beam of light is largely refracted and transmitted through the light-transmissive sheet body. Therefore, the amount of light that has passed through the light-transmissive sheet body is changed, and the defect is detected based on such a change in the amount of light transmitted through the light-transmissive sheet body.
The disclosed conventional process is effective to automatically detect relatively large defects of sheet bodies. However, it is difficult for the process to obtain a change in the amount of light which is caused by a small defect that can visually be judged by a skilled worker.
Therefore, it has been customary for a skilled worker to cut off a portion of the sheet body as a sample, develop an image on the sample, and determine whether there is a defect in the sample or not based on the developed negative, or to dispense with these steps and discard a relatively long sheet body portion including large safety margins.
However, the customary process of inspecting samples is time-consuming, and is further disadvantageous in that even skilled workers are likely to determine different sheet body lengths to be thrown away based on inspected results because the different skilled workers have different individual tendencies. The alternative process of discarding a relatively long sheet body portion including large safety margins is not preferable because normal areas are necessarily included in the discarded sheet body length.